Note: Descriptions are shown in the official language in which they were submitted.
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ACTIVELY CONTROLLED ROTARY STEERABLE
SYSTEM AND METHOD FOR DRILLING WELLS
BACKGROUND OF THE INVENTION
Field of the Invention
This invention relates generally to methods and
apparatus for drilling wells, particularly wells for the
production of petroleum products, and more specifically
concerns an actively controlled rotary steerable drilling
system that can be connected directly to a rotary drill
string or can be connected in a rotary drill string in
assembly with a mud motor and/or thruster and/or flexible
sub to enable selective decoupling of the actively
controlled rotary steerable drilling system from the rotary
drill string, such as for mud motor powered drilling, with
or without drill string rotation, and to enable precision
control of the direction of a bore being drilled by a drill
bit and precision control of the rotary speed, torque and
weight on bit being imparted to the drill bit. For mud
motor speed and torque control, a controllable dump valve is
provided in the fluid circuitry of the mud motor to
controllably dump or divert a portion of the drilling fluid
flow from the fluid circuit of the mud motor to the annulus
or to bypass a portion of the drilling fluid flow past the
rotor of the mud motor. This mud motor dump or bypass
control valve can be automatically operated responsive to
sensor signals from the rotary steerable drilling system or
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can be operated responsive to signals from the surface or both. For
controlling weight on bit a
drilling fluid powered thruster is provided in the drill string and is located
above or below the
rotary steerable drilling system. The thruster has a similarly controllable
dump or bypass valve in
its drilling fluid circuitry which is selectively adjustable by the control
circuitry of the rotary
steerable drilling system for the purpose of controlling the downward
mechanical force, i.e.,
weight of the drill bit against the formation being drilled. The dump or
bypass valves of the mud
motor and thruster are thus both independently controlled downhole by the
control system of the
rotary steerable drilling tool responsive to feedback signals from various
sensors and can be
selectively controlled by telemetry from the surface as well. This invention
also concerns an
actively controlled rotary steerable drilling system incorporating a turbine
powered electric motor
drive mechanism for geostationary positioning of a drill bit during its
rotation by the rotary drill
string, mud motor, or both and having the capability for selective employment
of the electric
motor as a brake when the torque of the bit/formation interaction is prevalent
as compared to
internal friction.
Description of the Related Art:
An oil or gas well often has a subsurface section that is drilled
directionally, i.e., inclined
at an angle with respect to the vertical and with the inclination having a
particular compass
heading or azimuth. Although wells having deviated sections may be drilled at
any desired
location, such as for "horizontal" borehole orientation or deviated branch
bores from a primary
borehole, for example, a significant number of deviated wells are drilled in
the marine
environment. In such case, a number of deviated wells are drilled from a
single offshore
production platform in a manner such that the bottoms of the boreholes are
distributed over a large
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area of a producing horizon over which the platform is typically centrally
located and wellheads
for each of the wells are located on the platform structure.
Whether well drilling is being done on land or in a marine environment, there
exists a
present need in well drilling activities for extended reach drilling, which is
accomplished
S according to the teachings of the present invention by achieving better
transfer of weight and
torque to the drill bit during drilling operations. High performance/power
drilling is also achieved
by the present invention by causing good transfer of weight and torque to the
drill bit being
controlled by the rotary steerable drilling system set forth in detail below.
In circumstances where
the well being drilled is of complex trajectory, the capability provided by
the rotary steerable
drilling system of this invention to steer the drill bit while the drill bit
is being rotated by the
collar of the tool enables drilling personnel to readily navigate the wellbore
from one subsurface
oil reservoir to another. The rotary steerable drilling tool enables steering
of the wellbore both
from the standpoint of inclination and from the standpoint of azimuth so that
two or more
subsurface zones of interest can be controllably intersected by the wellbore
being drilled.
1 S A typical procedure for drilling a directional borehole is to remove the
drill string and drill
bit by which the initial, vertical section of the well was drilled using
conventional rotary drilling
techniques, and run in at the lower end of the drill string a mud motor having
a bent housing
which drives the bit in response to circulation of drilling fluid. The bent
housing provides a bend
angle such that the axis below the bend point, which corresponds to the
rotation axis of the bit,
has a "toolface" angle with respect to a reference, as viewed from above. The
toolface angle, or
simply "toolface", establishes the azimuth or compass heading at which the
deviated borehole
section will be drilled as the mud motor is operated. After the toolface has
been established by
slowly rotating the drill string and observing the output of various
orientation devices, the mud
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motor and drill bit are lowered, with the drill string non-rotatable to
maintain the selected
toolface, and the drilling fluid pumps, "mud pumps", are energized to develop
fluid flow through
the drill string and mud motor, thereby imparting rotary motion to the mud
motor output shaft and
the drill bit that is fixed thereto. The presence of the bend angle causes the
bit to drill on a curve
until a desired borehole inclination has been established. To drill a borehole
section along the
desired inclination and azimuth, the drill string is then rotated so that its
rotation is superimposed
over that of the mud motor output shaft, which causes the bend section to
merely orbit around the
axis of the borehole so that the drill bit drills straight ahead at whatever
inclination and azimuth
have been established. If desired, the same directional drilling techniques
can be used as the
maximum depth of the wellbore is approached to curve the wellbore to
horizontal and then extend
it horizontally into or through the production zone. Measurement-while-
drilling "MWD" systems
commonly are included in the drill string above the mud motor to monitor the
progress of the
borehole being drilled so that corrective measures can be instituted if the
various borehole
parameters indicate variance from the projected plan.
Various problems can arise when sections of the well are being drilled with
the drill string
non-rotatable and with a mud motor being operated by drilling fluid flow. The
reactive torque
caused by operation of a mud motor can cause the toolface to gradually change
so that the
borehole is not being deepened at the desired azimuth. If not corrected, the
wellbore may extend
to a point that is too close to another wellbore, the wellbore may miss the
desired "subsurface
target", or the wellbore may simply be of excessive length due to "wandering".
These undesirable
factors can cause the drilling costs of the wellbore to be excessive and can
decrease the drainage
efficiency of fluid production from a subsurface formation of interest.
Moreover, a non-rotating
drill string may cause increased frictional drag so that there is less control
over the "weight on bit"
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and the rate of drill bit penetration can decrease, which can result in
substantially increased
drilling costs. Of course, a non-rotating drill string is more likely to get
stuck in the wellbore than
a rotating one, particularly where the drill string extends through a
permeable zone that causes
significant build up of mud cake on the borehole wall.
S Two patents of interest to the subject matter of the present invention are
U.S. Patents
5,113,953 and 5,265,682. The '953 patent presents a directional drilling
apparatus and method in
which the drill bit is coupled to the lower end of a drill string through a
universal joint, and the bit
shaft is pivotally rotated within the steerable drilling tool collar at a
speed which is equal and
opposite to the rotational speed of the drill string. The present invention is
significantly advanced
as compared to the subject matter of the '953 patent in that the angle of the
bit shaft or mandrel
relative to the drill collar of the present invention is variable rather than
being fixed.
Additionally, the provision of a braking system (electrical, mechanical or
hydraulic) in the rotary
steerable drilling tool of the present invention is another significant
advance over the teachings of
the prior art. Even further, the presence of various position measurement
systems and position
signal responsive control in the rotary steerable drilling system of the
present invention
distinguishes it from the prior art. The present invention is also
distinguished from the teachings
of the prior art in the assembly of drilling system controllable mud motor and
thruster apparatus
and a flexible sub that can be arranged in any suitable assembly to enable
directionally controlled
drilling to be selectively powered by the rotary drill string, the mud motor,
or both, and to provide
for precision control of weight on bit and accuracy of drill bit orientation
during drilling.
The '682 patent presents a system for maintaining a downhole instrumentation
package in
a roll stabilized orientation by means of an impeller. The roll stabilized
instrumentation is used
for modulating fluid pressure to a set of radial pistons which are
sequentially activated to urge the
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bit in a desired direction. The drill bit steering system
of the '682 patent most notably differs from the concept of
the present invention in the different means that is
utilized for deviating the drill bit in the desired
direction. Namely, the '682 patent describes a mechanism
which uses pistons to force the bit in a desired lateral
direction within the borehole. In contrast, the rotary
steerable drilling system of the present invention keeps the
drill bit pointing in a desired borehole direction, despite
rotation of the drill collar, by utilizing an impeller to
drive an alternator, the output of which drives an electric
motor to rotate the bit shaft axis about a universal joint
at the same rotational frequency as the bit shaft is driven
in rotary manner by the tool collar. The rotary steerable
drilling system of the present invention also utilizes a
braking system (electrical, hydraulic or mechanical) to
control the rotation of the bit shaft when the torque of the
bit/formation interaction is prevalent as compared to
internal friction. Within the scope of the present
invention the sensors and electronics of the tool may be
rotated along with the drilling tool collar or may be
maintained geostationary along with the axis of the bit
shaft of the rotary steerable drilling system.
SLIN~iARY OF THE INVENTION
In one aspect of the invention, there is provided
a method for drilling a well and simultaneously steering a
drill bit with an actively controlled rotary steerable
drilling system, comprising: rotating a tool collar
connected to a drill string, said tool collar defining a
longitudinal axis; with bit shaft positioning means,
pivotally rotating a bit shaft supported within said tool
collar for rotational movement about a pivot point within
said tool collar and in a direction counter to rotation of
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said tool collar, said bit shaft being rotatably driven by
said tool collar and being adapted for supporting a drill
bit; transmitting steering control signals to said bit shaft
positioning means causing synchronous pivotal counter-
s rotation of said bit shaft by said bit shaft positioning
means about said pivot point with respect to rotation of
said tool collar, and maintaining said longitudinal axis of
said bit shaft substantially geostationary and selectively
axially inclined relative to the longitudinal axis of said
tool collar during rotation of said bit shaft by said tool
collar; and selectively rotationally braking said bit shaft
positioning means in reference to external disturbances
acting to divert said drill bit from its projected course.
In a second aspect of the invention, there is
provided a method for drilling a well and simultaneously
steering a drill bit with an actively controlled rotary
steerable drilling system, comprising: rotating a tool
collar connected to a drill string, said tool collar
defining a longitudinal axis; with bit shaft positioning
means, counter-rotating a bit shaft supported for rotational
movement about a pivot point within said tool collar, said
bit shaft being rotatably driven by said tool collar and
being adapted for supporting a drill bit; dynamically
sensing the angular position of said longitudinal axis of
said bit shaft relative to said longitudinal axis of said
tool collar, the position of said tool collar with respect
to the earth and the orientation of said longitudinal axis
of said bit shaft relative to said tool collar and providing
position signals; and processing said position signals and
developing steering control signals causing synchronous
pivotal counter-rotation of said bit shaft about said pivot
point by said bit shaft positioning means with respect to
rotation of said tool collar for maintaining said
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longitudinal axis of said bit shaft substantially
geostationary and selectively axially inclined relative to
the longitudinal axis of said tool collar during rotation of
said bit shaft by said tool collar; and selectively
rotationally braking said bit shaft positioning means in
reference to external disturbances acting to divert said
drill bit from its projected course.
In,a third aspect of the invention, there is
provided a method for drilling a wellbore with a rotary
steerable drilling system connected to a drill string while
simultaneously selectively orienting a drill bit being
rotated thereby, comprising: rotating a tool collar with a
rotating drill string, said tool collar defining a
longitudinal axis and having a bit shaft pivotally mounted
therein, said bit shaft defining a longitudinal axis
disposed for omnidirectional pivotal movement relative to
said tool collar; operating a turbine within said tool
collar with drilling fluid flowing through said tool collar
and rotating an output shaft of said turbine; driving an
alternator with said output shaft of said turbine and
producing an electrical output of said alternator; operating
an electric motor with said electrical output of said
alternator and with a rotary output shaft of said electric
motor driving an offsetting mandrel within said tool collar
in synchronous pivotal counter-rotational relation with tool
collar rotation and translating rotary motion of said
offsetting mandrel into pivotal movement of said bit shaft
within said tool collar for geostationary orientation of
said longitudinal axis of said bit shaft in selected angular
relation with said longitudinal axis of said tool collar for
drilling a curved wellbore; and selectively rotationally
braking said offsetting mandrel in reference to external
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disturbances acting to divert said drill bit from its
projected course.
In a fourth aspect of the invention, there is
provided a method for drilling a wellbore with a rotary
steerable drilling system connected to a drill string while
simultaneously selectively orienting a drill bit being
rotated thereby, comprising: rotating a tool collar with a
rotating drill string, said tool collar defining a
longitudinal axis and having a bit shaft pivotally mounted
therein, said bit shaft defining a longitudinal axis
disposed for omnidirectional pivotal movement relative to
said tool collar; operating a turbine within said tool
collar with drilling fluid flowing through said tool collar
and rotating an output shaft of said turbine; driving an
alternator with said output shaft of said turbine and
producing an electrical output of said alternator; operating
an electric motor with said electrical output of said
alternator and with a rotary output shaft of said electric
motor driving an offsetting mandrel within said tool collar
in synchronous pivotal counter-rotational relation with tool
collar rotation, said offsetting mandrel defines an
eccentric receptacle having at least one eccentric ring
therein and said bit shaft is engaged within said eccentric
ring and translating rotary motion of said offsetting
mandrel into pivotal movement of said bit shaft within said
tool collar for geostationary orientation of said
longitudinal axis of said bit shaft in selected angular
relation with said longitudinal axis of said tool collar for
drilling a curved wellbore; and selectively adjusting the
relative position of said eccentric ring with respect to
said eccentric receptacle for selectively establishing said
angular relation of said longitudinal axis of said bit shaft
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relative to said longitudinal axis of said tool collar at a
selected angle between 0 and a predetermined angle.
In a fifth aspect of the invention, there is
provided a method for drilling a wellbore with a rotary
steerable drilling system while simultaneously selectively
orienting a drill bit being rotated by a rotatable tool
collar of said rotary steerable drilling system, said tool
collar defining a longitudinal axis and connected for
rotation by a drill string of well drilling equipment,
comprising: rotating said tool collar having a bit shaft
mounted therein for pivotal movement relative to said tool
collar, said bit shaft defining a longitudinal axis and
being rotatably driven by said tool collar; counter-rotating
an offsetting mandrel within said tool collar, said
offsetting mandrel having an offset driving connection with
said bit shaft and translating rotary motion of said
offsetting mandrel into rotary pivoting of said bit shaft
about a pivot point within said tool collar; applying
braking for maintaining said longitudinal axis of said bit
shaft geostationary and in predetermined angular relation
with said longitudinal axis of said tool collar; and
selectively orienting said longitudinal axis of said bit
shaft in angular relation with said longitudinal axis of
said tool collar for causing the drill bit to drill a curved
wellbore in a selected direction.
In a sixth aspect of the invention, there is
provided a method for drilling a wellbore with an actively
controlled rotary steerable drilling system, comprising:
rotating a tool collar connected to a drill string, said
tool collar defining a longitudinal axis; imparting driving
rotation to a bit shaft pivotally supported by said tool
collar for pivotal movement of the longitudinal axis thereof
about a pivot point relative to the longitudinal axis of
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said tool collar; driving a turbine mounted within said tool
collar by drilling fluid flow through said tool collar, said
turbine having rotary driving connection with an offsetting
mandrel mounted for rotation within said tool collar, said
offsetting mandrel imparting pivotal counter-rotation to
said bit shaft at the same rotary frequency as rotation of
said tool collar and establishing a selected angular
relation of said longitudinal axis of said bit shaft with
said longitudinal axis of said tool collar; and selectively
applying braking force for maintaining said longitudinal
axis of said bit shaft substantially geostationary and
selectively axially inclined with respect to said
longitudinal axis of said tool collar for selectively
steering said drill bit and the wellbore being drilled
thereby.
In a seventh aspect of the invention, there is
provided an actively controlled rotary steerable drilling
system for well drilling, comprising: a tool collar being
adapted for connection to a drill string for rotation by the
drill string and defining a longitudinal axis; a bit shaft
being supported within said tool collar for pivotal movement
about a pivot point and being rotatably driven by said tool
collar, said bit shaft defining a longitudinal axis and
being adapted for supporting a drill bit; a bit shaft
position sensor within said tool collar for dynamically
sensing the angular position of said longitudinal axis of
said bit shaft relative to said longitudinal axis of said
tool collar and providing bit shaft position signals; system
electronics processing said bit shaft position signals of
said bit shaft position sensor and causing synchronous
pivotal counter-rotation of said bit shaft about said pivot
point with respect to rotation of said tool collar and
maintaining said longitudinal axis of said bit shaft
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substantially geostationary and selectively axially inclined
relative to the longitudinal axis of said tool collar during
rotation of said bit shaft by said tool collar; and a brake
within said tool collar for applying a braking force for
maintaining said longitudinal axis of said bit shaft
substantially geostationary and selectively axially inclined
with respect to said longitudinal axis of said tool collar
for selectively steering said drill bit and the wellbore
being drilled thereby.
It is a feature of the present invention to
provide a novel drilling system that is driven by a rotary
drill string and permits selective drilling of curved
wellbore sections by precision steering of the drill bit
being rotated by the drill string and drilling tool.
It is also a feature of the present invention to
provide a novel actively controlled rotary steerable well
drilling system having a bit shaft that is rotatably driven
by the collar during drilling and which is mounted
intermediate its length for omnidirectional pivotal movement
within the collar for the purpose of geostationary
positioning of the bit shaft and drill bit relative to the
tool collar to thereby continuously point the drill bit
supported thereby at a desired angle for
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CA 02291600 1999-12-06
the drilling of a curved wellbore;
It is another feature of the present invention to provide a novel actively
controlled rotary
steerable well drilling system having an offsetting mandrel which is rotated
counter to the
direction of rotary movement of the tool collar and at the same frequency of
rotation, thus
S imparting rotary motion to the bit shaft about its omnidirectional pivotal
mount to maintain the bit
shaft geostationary;
It is another feature of the present invention to provide a novel actively
controlled rotary
steerable well drilling system having within the tool a drilling fluid powered
turbine that is
connected in driving relation with an alternator for generation of sufficient
electrical power to
drive a motor that counteracts the resistive torque between the collar or
housing of the drilling
tool and the offsetting mandrel that counter-rotates within the tool collar
and accomplishes
geostationary positioning of the movable bit shaft for the purpose of drill
bit steering;
It is another feature of the present invention to provide a novel actively
controlled rotary
steerable well drilling system having on-board electronic power and control
system circuitry that
is mounted throughout the length of the tool and is rotatable along with the
drill string driven tool
collar;
It is an even further feature of the present invention to provide a novel
actively controlled
rotary steerable well drilling system having sensors and electronics that are
rotatable along with
the drill collar thereof or geostationary in line with the offsetting mandrel
thereof;
It is also a feature of the present invention to provide a novel actively
controlled rotary
steerable well drilling system having therein an electrically, hydraulically,
or mechanically
controlled braking system for maintaining the offsetting mandrel and bit shaft
axis geostationary
during drilling;
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CA 02291600 1999-12-06
It is an even further feature of the present invention to provide an
embodiment of the
actively controlled rotary steerable well drilling system having a brake that
controls the drilling
fluid powered turbine and which is controlled based on the real-time
measurement of the toolface;
and
S It is another feature of an embodiment of the present invention to provide a
novel actively
controlled rotary steerable well drilling system having a transmission
mechanism interconnecting
the brake and the drilling fluid powered turbine and providing for appropriate
dissipation of
energy by the brake while allowing the drilling fluid powered turbine to
operate at an efficient
rotary speed for optimum generation of power.
Briefly, the various objects and features of the present invention are
realized through the
provision of an actively controlled rotary steerable drilling tool having a
collar or housing that is
connected directly to a rotary drill string that is driven by the rotary table
of a drilling rig. Though
the description herein is directed particularly to an electronically energized
and actively controlled
rotary steerable drilling tool, it is not intended to so restrict the present
invention. This invention
is equally applicable to hydraulically controlled rotary steerable drilling
tools and rotary steerable
drilling tools incorporating both electronic and hydraulic control features. A
bit shaft having a
drill bit connected thereto is mounted within the collar by means of an
omnidirectional mount and
is rotatable directly by the tool collar for the purpose of drilling. A lower
section of the bit shaft
projects from the lower end of the collar and provides support for the drill
bit. According to the
concept of this invention, the bit shaft axis is counter-rotated with respect
to the tool collar about
its pivotal mount and is thus maintained pointed in a given direction, which
is inclined by a
variable angle with respect to the axis of the tool, thus allowing the drill
bit to drill a wellbore on a
curve that is determined by the selected angle. A straight bore can be drilled
either by setting the
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CA 02291600 1999-12-06
angle between the bit shaft axis and the tool axis to zero or by rotating the
bit shaft axis around
the tool axis at a different frequency. The angle between the axis of the bit
shaft and the axis of
the collar of the drilling tool is obtained by means of an offsetting mandrel
which counter-rotates
with respect to the collar and which maintains the bit shaft axis
geostationary. The rotary steerable
drilling tool of the present invention incorporates a mechanism that is
operated downhole for
controllably changing this angle as desired for the purpose of controllably
steering the drill bit
being rotated by the tool. Torque is transmitted from the tool collar to the
bit shaft directly
through the universal joint. As the collar is rotated by the drill string, the
resistive torque Ties
acting between the collar and the offsetting mandrel and its supports, which
is mainly due to
friction, tends to rotate the offsetting mandrel together with the collar so
that an over-gauge hole
would be drilled. To prevent this or, more specifically, to keep the bit shaft
geostationary despite
the rotation of the collar, an electric motor powered by a mud powered turbine
and alternator is
employed which generates enough power to counteract the resistive torque. An
electric, hydraulic
or mechanical brake is employed to counteract the effect of the interaction
between the formation
and the bit, which interaction could result in a torque opposite to the
internal resistive torque of
the rotary steerable drilling system. In addition, the motor and the brake are
servo-controlled to
guarantee that the toolface is maintained in the presence of external
disturbances. Since it should
always remain geostationary, the offsetting mandrel should always be pivotally
rotated at a speed
equal and opposite the rotational speed of the collar, with respect to the
collar. In another
embodiment of this invention a drilling fluid powered turbine is connected in
driving relation with
the electromagnetic brake. To allow the turbine to rotate at higher speeds
more suited to the
operation of an axial turbine, a transmission mechanism having a gear train is
used between the
turbine and the offsetting mandrel so that the offsetting mandrel is rotated
at a slower speed and
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CA 02291600 1999-12-06
with enhanced power for achieving geostationary positioning of the bit shaft.
To enhance the flexibility of the actively controlled rotary steerable
drilling tool, the tool
has the capability of selectively incorporating many electronic sensing,
measuring, feedback and
positioning systems. A three-dimensional positioning system of the tool can
employ magnetic
S sensors for sensing the earth's magnetic field and can employ accelerometers
and gyroscopic
sensors for accurately determining the position of the tool at any point in
time. For control the
rotary steerable drilling tool will typically be provided with three
accelerometers and three
magnetometers. A single gyroscopic sensor will typically be incorporated
within the tool to
provide rotational speed feedback and to assist in stabilization of the
mandrel, although a plurality
of gyroscopic sensors may be employed as well without departing from the
spirit and scope of this
invention. The signal processing system of the electronics on-board the tool
achieves real time
position measurement while the tool is rotating and while it is rotating the
bit shaft and drill bit
during drilling operations. The sensors and electronics processing system of
the tool also
provides for continuous measurement of the azimuth and the actual angle of
inclination as drilling
progresses so that immediate corrective measures can be taken in real time,
without necessitating
interruption of the drilling process. The tool incorporates a position based
control loop using
magnetic sensors, accelerometers and gyroscopic sensors to provide position
signals for
controlling the motor and the brake of the tool. With regard to braking, it
should be borne in mind
that the electric motor for driving the offsetting mandrel also is
controllable by the internal control
system of the tool to provide a braking function as needed to counteract the
effect of the
interaction between the formation and the drill bit resulting in torque that
is opposite to the
internal resistive torque of the tool. Also from the standpoint of operational
flexibility, the tool
may incorporate a measuring while drilling (MWD) system for feedback, positive
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CA 02291600 1999-12-06
motor/turbine, gamma ray detectors, resistivity logging, density and porosity
logging, sonic
logging, borehole imaging, look ahead and look around instrumentation,
inclination at the bit
measurement, bit rotational speed measurement, vibration below the motor
sensors, weight on bit,
torque on bit, bit side force, a soft weight system with a thruster controlled
by the tool to
S maximize drilling efficiency, a variable gauge stabilizer controlled by the
tool, or a mud motor
dump valve controlled from the tool to control drilling speed and torque. The
tool may also
incorporate other measurement devices that are useful for well drilling and
completion.
The design of the tool adds downhole soft-torque intrinsically to minimize bit
wear and to
achieve maximum drilling efficiency. Software is employed in the operational
control system
electronics on-board the tool to minimize stick-slip. Additionally, the tool
provides the possibility
of programming the tool from the surface so as to establish or change the tool
azimuth and
inclination and to establish or change the bend angle relation of the bit
shaft to the tool collar.
The electronic memory of the on-board electronics of the tool is capable of
retaining, utilizing and
transmitting a complete wellbore profile and accomplishing geosteering
capability downhole so it
can be employed from kick-off to extended reach drilling. Additionally, a
flexible sub may be
employed with the tool to decouple the rotary steerable drilling tool from the
rest of the bottom-
hole assembly and drill string and allow navigation from the rotary steerable
drilling system.
In addition to other sensing and measuring features of this invention, the
actively
controlled rotary steerable drilling tool may also be provided with an
induction telemetry coil or
coils to transmit logging and drilling information that is obtained during
drilling operations to the
MWD system bidirectionally through the flexible sub, the motor, the thruster
and other
measurement subs. For induction telemetry the rotary steerable drilling tool
typically incorporates
an inductor within the tool collar. The tool also incorporates transmitters
and receivers located in
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predetermined axially spaced relation to thus cause
signals to traverse a predetermined distance through the
subsurface formation adjacent the wellbore and thus
measure its resistivity. Such a system is described in
U.S. Patent 5,594,343.
The electronics of the resistivity system of the
tool, as well as the electronics of the various measurement
and control systems, are capable of rotation along with
rotary components of the tool and will thus withstand the
effects of drill string rotation as well. In the
alternative, certain components of the electronics system of
the rotary steerable drilling tool may be geostationary.
In the preferred embodiment of the present
invention a drilling fluid driven turbine is interconnected
in driving relation with an alternator to develop electrical
energy from the power of the flowing drilling fluid. For
optimum turbine and alternator operation a mechanical
transmission may be interposed between the turbine and the
alternator. An electric motor, which is not mechanically
interconnected with the turbine or alternator, has its
electrical supply input connected to the electrical output
of the alternator, with an electrical control system being
in assembly with the motor for its operational control. In
addition, a brake which is not mechanically interconnected
with the turbine or alternator is available to maintain the
bit shaft axis geostationary when the formation friction
effect prevails. The rotary output of the motor is used to
drive the geostationary mandrel of the rotary steerable
drilling tool, thus turbine and alternator operation cannot
interfere directly with operation of the motor and bit shaft
orientation control. For the purpose of mechanical
efficiency, according to the preferred embodiment, the bit
12
CA 02291600 2004-09-15
50952-14
shaft positioning system employs a universal bit shaft
support employing balls and rings establishing a hook-like
joint which provides the bit shaft with both efficient
support in the axial direction and torque and at the same
time minimizes friction at the universal joint. Friction of
the
12a
CA 02291600 1999-12-06
universal joint is also minimized by ensuring the presence of lubricating oil
about the components
thereof and by excluding drilling fluid from the universal joint while
permitting significant
cyclical steering control movement of the bit shaft relative to the tool
collar as drilling is in
progress. Alternatively, instead of the ball and ring type universal joint,
the universal joint may
take the form of a spline type joint or a universal joint incorporating
splines and rings.
The electric motor of the rotary steerable drilling system is powered by
electric current
that is generated by drilling fluid flow through a turbine. To control the
electrical power output
the turbine can have variable efficiency, which is achieved by moving the
stator relative to the
rotor. The turbine may also have multiple stages or it may be provided with
braking such as by a
resistor load.
BRIEF DESCRIPTION OF THE DRAWINGS
So that the manner in which the above recited features, advantages and objects
of the
present invention are attained can be understood in detail, a more particular
description of the
invention, briefly summarized above, may be had by reference to the preferred
embodiment
thereof which is illustrated in the appended drawings, which drawings are
incorporated as a part
hereof.
It is to be noted however, that the appended drawings illustrate only a
typical embodiment
of this invention and are therefore not to be considered limiting of its
scope, for the invention may
admit to other equally effective embodiments.
In the Drawings:
Fig. 1 is a schematic illustration showing a well being drilled in accordance
with the
present invention and showing deviation of the lower portion of the wellbore
by the actively
13
CA 02291600 1999-12-06
controlled rotary steerable drilling system and method hereof;
Fig. 2 is a schematic illustration showing a well being drilled by the
actively controlled
rotary steerable drilling system and method hereof and employing in the rotary
drill string a mud
motor located above the actively controlled rotary steerable drilling system
and rotating the tool
S collar of the steerable drilling system at a speed that is different from
the rotary speed of the drill
string;
Fig. 3 is a schematic illustration similar to that of Fig. 2 and showing the
mud motor
located below the actively controlled rotary steerable drilling system and
providing for direct
rotation of the drill bit at a speed different from the drill string;
Fig. 4 is a schematic illustration showing a thruster being located in the
drill string
immediately above the actively controlled rotary steerable drilling system for
controlling weight
on bit while rotary drilling speed and torque are being controlled by the
rotary steerable drilling
system;
Fig. 5 is a schematic illustration showing a thruster being located in a drill
string
immediately below the actively controlled rotary steerable drilling system;
Fig. 6 is a schematic illustration showing a thruster being located in a drill
string
immediately below a mud motor and connected above the actively controlled
rotary steerable
drilling system and providing for rotation of the rotary steerable drilling
system at a rotational
speed that differs from that of the drill string;
Fig. 7 is a schematic illustration showing a thruster located in a drill
string immediately
above a mud motor and with the mud motor located above the actively controlled
rotary steerable
drilling system;
Fig. 8 is a schematic illustration showing the actively controlled rotary
steerable drilling
14
CA 02291600 1999-12-06
system located in a drill string and showing a mud motor connected below the
rotary steerable
drilling system and a thruster connected below the mud motor so that the mud
motor provides
support for the drill bit;
Fig. 9 is a schematic illustration showing the actively controlled rotary
steerable drilling
system located in a drill string and showing a thruster connected below the
rotary steerable
drilling system and further showing a mud motor connected below the thruster
and supporting the
drill bit;
Fig. 10 is a schematic illustration of the rotary steerable drilling system of
the present
invention having a flexible sub interconnected in the drill string therewith
and showing bending of
the flexible sub;
Fig. 11 is a schematic illustration of the rotary steerable drilling system of
Fig. 10 and
showing the straight condition of the flexible sub;
Fig. 12 is a schematic illustration in longitudinal section showing an
actively controlled
rotary steerable drilling system representing the preferred embodiment of the
present invention
and having a turbine driven alternator, with the electric current output
thereof being utilized to
drive an electric motor having a motor output shaft connected in driving
relation with an
omnidirectional bit shaft support and positioning mechanism for maintaining
the longitudinal axis
of the bit shaft geostationary and at a predetermined angle relative to the
axis of rotation of the
tool collar;
Fig. 13 is a schematic illustration in section showing a turbine which may be
utilized for
the turbines of Figs. 12 and 14, and illustrating turbine stator positioning
relative to the rotor for
controlling the efficiency and power output of the turbine;
Fig. 14 is a schematic longitudinal sectional view of an actively controlled
rotary steerable
CA 02291600 1999-12-06
drilling system representing an alternative embodiment of the present
invention and showing a
turbine connected in driving relation with an alternator and with the turbine
and alternator being
located in the same section of the tool collar as the motor, offsetting
mandrel and bit shaft and
further showing a mechanism providing omnidirectional pivotal support within
the tool collar for
the bit shaft;
Fig 15 is a schematic longitudinal sectional view of an actively controlled
rotary steerable
drilling system representing an alternative embodiment of the present
invention and showing a
turbine connected in driving relation with a gear box via a turbine drive
shaft extending through
the electronics, sensors and brake section of the drilling system and with the
output of the gear
box connected in driving relation with an offsetting mandrel for accomplishing
geostationary
positioning of the axis of a bit shaft;
Fig. 16 is a partial longitudinal sectional view illustrating a further
alternative embodiment
of the present invention showing a rotary steerable drilling tool having a
hydraulically powered
system for orienting the bit shaft of the tool during drilling operations;
Fig. 17 is a longitudinal sectional view showing the lower portion of the
actively
controlled rotary steerable drilling system of Fig. 12 in greater detail;
Fig. 18 is a longitudinal sectional view showing the upper portion of the
actively
controlled rotary steerable drilling system of Fig. 12 in greater detail;
Fig. 19 is a transverse sectional view taken along line 19-19 of Fig. 17;
Fig. 20 is a transverse sectional view taken along line 20-20 of Fig. 18;
Fig. 21 is a partial transverse sectional view of an alternative embodiment of
the present
invention showing a spline type universal joint for omnidirectional support of
the bit shaft within
the tool collar and for imparting driving rotation to the bit shaft for
rotation of the drill bit;
16
CA 02291600 1999-12-06
Fig. 22A is a schematic illustration in transverse section showing the bit
shaft positioning
rings relatively positioned for straight drilling and showing coincidence of
the longitudinal axes of
the bit shaft and tool collar for zero angulation of the bit shaft;
Fig. 22B is a sectional view taken along line 22B-22B of Fig. 22A and showing
the
coaxial relationships of the bit shaft positioning rings for straight
drilling;
Fig. 22C is a schematic illustration in transverse section showing the bit
shaft positioning
rings located at positions for maximum offset and thus maximum lateral
positioning of the center-
line of the bit shaft for maximum angulation of the bit shaft relative to the
tool collar;
Fig. 22D is a sectional view taken along line 22D-22D of Fig. 22C showing the
offset
axial relationships of the bit shaft positioning rings for maximum offset and
thus drilling at
maximum rate of curvature;
Fig. 23 is a block diagram schematic illustration showing the control
architecture of the
preferred embodiment of the rotary steerable drilling system of the present
invention, showing the
concept of turbine powered braking and brake control for the purpose of
steering the drill bit that
is oriented by the tool;
Fig. 24 is a block diagram schematic illustration showing the control
architecture of an
alternative embodiment of the present invention having a drilling fluid
powered turbine and brake
for controlling bit shaft positioning relative to the tool collar and a
position signal responsive
brake controller for controlling the brake and for controlling turbine
efficiency; and
Fig. 25 is a transverse sectional view taken along line 25-25 of Fig. 21
showing a splined
drive connection between the bit shaft and drilling tool collar.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Refernng now to the drawings and first to Fig. 1, a wellbore 10 is shown being
drilled by a
17
CA 02291600 1999-12-06
rotary drill bit 12 that is connected at the lower end of a drill string 14
that extends upwardly to
the surface where it is driven by the rotary table 16 of a typical drilling
rig (not shown). The drill
string 14 typically incorporates a drill pipe 18 having one or more drill
collars 20 connected
therein for the purpose of applying weight to the drill bit 12. The wellbore
10 is shown as having
a vertical or substantially vertical upper section 22 and a deviated, curved
or horizontal lower
section 24 which is being drilled under the control of an actively controlled
rotary steerable
drilling tool shown generally at 26 which is constructed in accordance with
the present invention.
To provide the flexibility that is needed in the curved section 24 of the
wellbore 10 a lower
section of drill pipe 28 may be used to connect the drill collars 20 to the
drilling tool 26 so that the
drill collars will remain in the vertical section 22 of the wellbore 10. The
lower section 24 of the
wellbore 10 will have been deviated from the vertical section 22 by the
steering activity of the
drilling tool 26 in accordance with the principles set forth herein. As shown
at 28 in Fig. 1, the
drill string immediately adjacent the rotary steerable drilling tool, may
incorporate a flexible sub,
also shown in Figs. 10 and 11, which can provide the rotary steerable drilling
system with
enhanced accuracy of drilling. In accordance with the usual practice, drilling
fluid or "mud" is
circulated by surface pumps down through the drill string 14 where it exits
through jets that are
defined in the drill bit 12 and returns to the surface through an annulus 30
between the drill string
14 and the wall of the wellbore 10. As will be described in detail below, the
rotary steerable
drilling tool 26 is constructed and arranged to cause the drill bit 12 to
drill along a curved path
that is designated by the control settings of the drilling tool 26. The angle
of the bit shaft
supporting the drill bit 12 with respect to the tubular collar of the drilling
tool 26 is maintained
even though the drill bit and drilling tool are being rotated by the drill
string 14, thereby causing
the drill bit to be steered for drilling a deviated wellbore. Steering of the
drilling tool is
18
CA 02291600 1999-12-06
selectively accomplished from the standpoint of inclination and from the
standpoint of azimuth,
i.e., left and right. Additionally, the settings of the steerable drilling
tool 26 may be changed as
desired to cause the drill bit to selectively alter the course of the wellbore
being drilled to thereby
direct the deviated wellbore for precision steering of the drill bit and thus
precision control of the
S wellbore being drilled.
Figs. 2 and 3 are schematic illustrations showing the rotary steerable
drilling system of the
present invention located within a wellbore 10 being drilled and further
showing a method of
drilling wherein a mud motor M is utilized within the rotary drill string
either above the steerable
drilling tool as shown in Fig. 2 or below the steerable drilling tool as shown
in Fig. 3. This
unique arrangement permits rotation of the drill string 14 at a desired
rotational speed and rotation
of the mud motor output at a different rotational speed to provide for optimum
drilling
characteristics without causing excessive fatigue of the drill string. When
the rotary steerable
drilling system of the present invention is connected directly to the drill
string, the rotational
speed of the drill bit is the same as that of the drill string. This limits
the maximum rotational
speed of the drill bit because enhanced rotational speed of the drill string
could limit drill string
service life due to fatigue. When the mud motor M of Figs. 2 and 3 is run in
combination with the
rotary steerable drilling system, the rotary table of the drilling rig can be
set at an optimum
rotational speed for the drill string and the mud motor will be capable of
adding rotational speed
to the drill bit that is driven by the mud motor output. The rotary table can
be operated at a
rotational speed of SO revolutions per minute for example, to allow breaking
of the friction
between the borehole and the drill string, a rotational speed that will not
limit the service life of
the drill string due to fatigue, while the rotational speed of the drill bit
can be increased by the
mud motor to provide for enhanced drilling characteristics to thus enable
extended reach drilling.
19
CA 02291600 1999-12-06
The rotary steerable drilling system can be operated at the mud motor
controlled rotational speed
when located below the mud motor and can be rotated at drill string speed if
connected directly to
the drill string. If the mud motor is located below the rotary steerable
drilling tool, its rotary
output is imparted directly to the drill bit. Steering characteristics during
drilling will have greater
precision when the mud motor is located above the rotary steerable drilling
tool for the reason that
the distance from the rotary steerable drilling tool to the drill bit is a
principal controlling factor
from the standpoint of steering precision.
It should be borne in mind that the rotary steerable drilling system of the
present invention
may be connected in a drill string in association with other drilling tools
such as mud motors, as
described above, for controlling rotational speed and torque, and thrusters
for controlling weight
on bit. Moreover, the arrangement of these components within a drill string
may be selected by
drilling personnel according to a wide variety of characteristics, such as the
tightness of the
curved wellbore section being drilled, the characteristics of the formation
being drilled, the
character of drilling equipment being employed for drilling, and the depth at
which drilling is
taking place. The schematic illustration of Fig. 4 shows the rotary steerable
drilling tool 26
connected in the drill string 14 along with a drilling fluid powered thruster
T, which is provided to
control weight on bit. The thruster is comprised mainly of a hydraulically
controlled piston, the
lower part of the bottom hole assembly being connected to the piston. The
coupling 27 between
the rotary steerable drilling tool 26 and the thruster T may be a simple pipe
coupling, or a tool
section permitting integration of the control features, electronic, hydraulic,
or a combination of
electronic and hydraulic controls, between the rotary steerable drilling tool
and the thruster. If
desired, the coupling 27 may take the form of the flexible sub shown in Figs.
10 and 11. As
shown in Fig. 5, a thruster T is connected below the rotary steerable drilling
tool 26 and this is
CA 02291600 1999-12-06
positionable in angulated relation with the collar of the drilling tool 26 by
adjusting the position of
the bit shaft of the tool. In this case, the bit shaft provides support for
the thruster while the
thruster provides support for the drill bit as well as controlling weight on
bit. As shown in Fig. 6,
the arrangement of the rotary steerable drilling system 26 and the thruster T
is as shown in Fig. 4.
Additionally, a mud motor M is connected to the drill string 14 above the
thruster to thus provide
for rotation of the thruster and the collar of the rotary steerable drilling
tool at a speed of rotation
that is different from the rotational speed of the drill string, while at the
same time controlling
weight on bit. The schematic illustration of Fig. 7 shows a mud motor M
connected above the
rotary steerable drilling tool 26 and shows a thruster T connected in the
drill string 14 above the
mud motor. If desired, the coupling between either the rotary steerable
drilling tool and the mud
motor or between the mud motor and the thruster or both may be provided by a
flexible sub of the
character set forth in Figs. 10 and 11. Fig. 8 shows the rotary steerable
drilling tool connected to
the drill string 14 and having a mud motor M connected to the geostationary
bit shaft of the tool
and thus subject to angulation relative to the tool collar along with the bit
shaft. A thruster T is
located below the mud motor M for supporting the drill bit and for controlling
weight on bit. The
thruster T is positioned relative to the collar of the rotary steerable
drilling tool 26 by the output
shaft of the mud motor M and the mud motor is positioned for controlled
steering by the bit shaft
of the rotary steerable drilling tool. The schematic illustration of Fig. 9
shows the rotary steerable
drilling tool 26 connected to the drill string 14 and having a thruster T
supported and oriented by
the bit shaft relative to the collar of the tool. A mud motor M is positioned
below the thruster so
that its output shaft both supports and drives the drill bit. The drill bit is
thus steered by the rotary
steerable drilling tool and is rotationally driven by both the rotary speed of
the drill string and the
rotary speed of the mud motor output shaft. This enables the drill bit to be
rotated at a speed that
21
CA 02291600 1999-12-06
is greater than or equal to the rotational speed of the drill string, while at
the same time weight on
bit is controlled by the thruster.
As shown diagrammatically in Fig. 9, the thruster T may be provided with a
control valve
Dl in the fluid circuit thereof while a control valve D2 may be provided in
the fluid circuit of the
mud motor M. These control valves are selectively positioned by the control
circuitry of the
rotary steerable drilling system, indicated schematically by the line C, to
thus permit the thruster
and/or the mud motor to be integrated into the control system of the rotary
steerable drilling
system. In this manner the mud motor and thruster are subject to feedback
responsive control in
the same manner as the rotary steerable drilling system. The control valve D2
in the mud motor
M can be controlled by the rotary steerable drilling system to control the
rotary speed of the
output shaft of the mud motor and to thus control torque at the drill bit. The
control valve D1 of
the thruster is selectively positioned by the control system of the rotary
steerable drilling system
to control weight on bit. Thus, the rotary steerable drilling system of the
present invention
provides for effective steering of the drill bit and for enhanced drilling
characteristics by
efficiently controlling torque at the drill bit and controlling weight on bit
to thus promote
extended reach drilling.
Figs. 10 and 11 show a drill string 14 having an actively controlled rotary
steerable
drilling system 26 connected therein for steering a bit shaft having a drill
bit 12 connected thereto.
The drill string 14 also incorporates a mud motor M for increasing the speed
of rotation of the
drill bit 12 and a flexible sub 28 for the purpose of enhancing the precision
of steering that is
accomplished by the rotary steerable drilling system. The flexible sub 28 also
accomplishes
selective decoupling of the rotary steerable drilling system from the drill
string to thus enhance
the steering capability thereof.
22
CA 02291600 2004-09-15
50952-14
Referring to Figs. 12, 14 and 15, an actively
controlled rotary steerable drilling system constructed in
accordance with the principles of the present invention is
shown generally at 26, as mentioned above, and represents
the preferred embodiment. The actively controlled rotary
steerable drilling system 26 has a tubular collar 32 which
at its upper end defines an internally threaded section 34
enabling its connection directly to the flexible sub 28 or
to the rotary output shaft of a mud motor and thruster,
depending upon the manner by which the steerable drilling
tool 26 is to be employed. Referring to the alternative
embodiment of Fig. 14, within the upper portion of the
collar 32 there is provided an electromagnetic induction
system 36 and an electrical wire communication link 38 to
provide for communication of signals from the rotary
steerable drilling tool 26 to an uphole MWD system to send
downhole data back to the surface in real time and to
facilitate communication of control signals from drilling
control equipment at the surface to the tool during drilling
operations. The collar 32 also defines an electronics and
sensor support section 40 having therein various sensor
equipment. The support section 40 may define a
receptacle 42 within which is located a magnetometer,
accelerometer, and gyroscopic sensor having the capability
of providing electronic output signals that are utilized
dynamically for steering of the tool. A number of
electronic components of the actively controlled rotary
steerable drilling system 26 may also be incorporated within
the electronics and sensor support section 40. For example,
a formation resistivity measurement system 41 may be located
within the collar 32 for rotation along with the collar and
will incorporate vertically spaced transmitters and
receivers to enable electromagnetic signals to determine
23
CA 02291600 2004-09-15
50952-14
formation resistivity. The method and apparatus for
measuring resistivity of the earth formation being drilled,
and to do so while rotary drilling operations are in
progress, may conveniently take the form that is set forth
in U.S. Patent 5,594,343. The apparatus and electronics of
the
23a
CA 02291600 1999-12-06
resistivity measurement system may rotate with the collar 32 or it may rotate
with other
components of the actively controlled rotary steering tool. The system for
resistivity
measurement may also be physically located at any other desired location
within the tool 26 as
desired to enhance manufacture or use of the rotary steerable drilling system.
Various other
sensing and measuring systems may also be incorporated within the electronics
and sensor
support section 40, including, for example, a gamma ray measurement system or
a sonic imaging
system. The drilling tool 26 may also incorporate rotational speed sensing
equipment, bit shaft
vibration sensors and the like. Additionally, electronic data processing
systems may also be
included within the electronics package of the tool for receiving and
processing various data input
thereto and providing signal output that is used for steering control and for
controlling other
factors encountered during well drilling. The electronic data processing
systems may be
selectively located within the tool so as to be rotatable along with the tool
collar or counter-
rotatable within the tool collar along with the bit shaft and its operational
components.
As shown in Figs. 12 and 14, immediately above or below the electronics and
sensor
support section 40 there is provided a fluid energized turbine mechanism shown
generally at 48
having a stator 50 which is preferably disposed in fixed relation with the
tubular collar 32 and a
rotor 52 that is mounted for rotation relative to the stator 50. As shown in
Fig. 13, the relative
positions of the rotor 52 and stator 50 are adjustable, either or both of the
rotor and stator may be
subject to position controlling movement, for the purpose of controllably
varying the efficiency
and thus the power output of the turbine 48. The rotor 52 is provided with a
turbine output shaft
54 which is disposed in driving relation with an alternator 56 via a
transmission 58. Since the
turbine output shaft 54 is connected in driving relation with the transmission
58, turbine efficiency
control can be achieved by mounting the stator 50 so as to be controllably
movable by the drilling
24
CA 02291600 1999-12-06
system electronics responsive to turbine output demand. The turbine may also
be braked
electrically to limit free spin thereof, thus increasing the power that is
available from the turbine.
The heat that is developed during such electric braking will be dissipated
efficiently by the
drilling fluid which flows through the tool. The drilling fluid flow through
the tool also serves to
cool the various internal components of the tool, such as the electronics
package, the alternator
and the bit shaft positioning motor. In one embodiment of the present
invention the alternator 56,
as shown in Fig. 14, functions as resistance to turbine output and because of
its resistance, the
alternator 56 is utilized as an electromagnetic brake. In accordance with the
preferred
embodiment of this invention, the alternator 56 is provided with a
transmission mechanism 58
which permits the turbine 48 to operate at optimum rotational velocity for
efficient operation of
the alternator. The alternator 56 provides an electrical output that is
electrically coupled with the
operational and control circuitry of an electric motor 60 so that the
electrical energy generated by
the turbine driven alternator 56 is employed to drive the electric motor 60.
A gear box or transmission 61 driven by the electric motor 60 has its rotary
output
1 S connected in driving relation with an offsetting mandrel 62 which is
rotatably driven by the
internal rotor of the electric motor 60 and to which is fixed a rotary drive
head 64 having an
eccentrically located positioning receptacle 66 therein which receives an end
68 of a bit shaft 70.
The offsetting mandrel 62 and the rotary drive head 64 are counter-rotated
with respect to the
rotation of the collar 32 to maintain the axis of the bit shaft 70
geostationary during drilling. The
bit shaft 70 is mounted for rotation within the tubular collar 32 intermediate
its extremities for
omnidirectional movement about a pivot-like universal joint 72 which is
preferably of the ball
pivot configuration and function shown in Figs. 17 and 19 and described below,
and if desired,
may be of the splined configuration shown in Figs. 21 and 25, also described
in detail below.
CA 02291600 1999-12-06
Certain components of the electronic data processing systems may be located
geostationary in the
rotary drive head 64. For example, the accelerometers, magnetic sensors and
gyroscopic sensor
may be located in the rotary drive head 64. An inclination sensor is located
on the rotary drive
head 64 to thereby provide a measurement reflecting the position of the drive
head within the
borehole.
To permit accuracy of downhole steering of the rotary steerable drilling
system, the
precise position of the rotary components of the drilling tool establish a
known position index
from which steering correction is determined. As such, it is desirable that
position indicating
sensors be located in geostationary relation with respect to the rotary drive
system for the bit
shaft. Accordingly, the rotary drive head 64 of the offsetting mandrel 62 may
be provided with
various position indicators, such as accelerometers, magnetometers, and
gyroscopic sensors which
are disposed in fixed relation with the rotary drive head 64 or any other
component that is
rotatable concurrently therewith. These position indicating components
eliminate the need for
precision location of the drill string and the collar 32 of the rotary
steerable drilling system 26 as
the drilling operation progresses and facilitate real time position signal
feedback to the signal
processing package of the drilling system so that tracking corrections can be
established
automatically by the control system of the rotary steerable drilling system to
maintain the desired
course of the drill bit.
Referring now to the schematic illustration of Fig. 14, an alternative
embodiment of the
present invention is shown generally at 26A, wherein like components, as
compared to the
embodiment of Fig. 12, are shown by like reference numerals. It should be
borne in mind that the
basic difference in the embodiments of Figs. 12 and 14 is the location of the
turbine 48 and
alternator 56 with respect to the electronics and sensor support section 40 of
the rotary steerable
26
CA 02291600 1999-12-06
drilling system 26. Within the tubular tool collar 32, as shown in Fig. 14,
the electronics and
sensor support section 40 is located above the turbine 48. The stator 50 and
rotor 52 of the
turbine 48 of Fig. 14 can be relatively adjustable, with the stator 50
preferably being linearly
movable within the collar 32 relative to the rotor 52 to adjust the efficiency
and thus the power
output of the turbine. The turbine output shaft 54 is connected in driving
relation with an
alternator 56 which may have a transmission 58 for permitting the turbine and
alternator to run at
appropriate speeds for optimum torque output. The heat that is generated by
motor operation and
braking and by the system electronics will be continually dissipated by the
drilling fluid that flows
continuously through the rotary steerable drilling system. The alternator 56
powers an electric
motor 60. The output shaft of the electric motor 60 functions as an offsetting
mandrel 62 and is
provided with a rotary drive head 64 having a positioning receptacle 66
located eccentrically
therein and receiving the driven end 68 of a bit shaft 70 for rotating the bit
shaft about its
universal joint support 72 in the manner described above in connection with
the preferred
embodiment of Fig. 12. With regard to the omnidirectional or universal joint
support 72 for the
bit shaft 70, it should be borne in mind that the omnidirectional or universal
joint support may be
of the ball type as shown in Figs. 17 and 19, or of the splined type as shown
in Figs. 21 and 25.
Referring now to the schematic illustration of Fig. 15, another alternative
embodiment of
the present invention is shown generally at 26B, wherein like components, as
compared to the
embodiment of Fig. 12, are also shown by like reference numerals. The rotary
steerable drilling
system 26B incorporates an elongate, tubular tool collar 32 which is adapted
for connection to a
drill string or rotary components of a drill string so that the tool collar 32
is rotated during well
drilling operations. Within the tool collar 32 a turbine, shown generally at
48 is mounted and
includes a rotor and stator assembly, with the rotor being driven by drilling
fluid flow 49 through
27
CA 02291600 1999-12-06
the tool collar. As shown schematically, the electronics and sensors and the
brake mechanism 35
of the rotary steerable drilling system are secured within the tool collar 32
by mounting elements
33 so that an annulus 37 exists which defines a flow path through which
drilling fluid is allowed
to flow. Heat that is developed in the electronics and sensors and brake
mechanism 35 during
operation is carried away by the drilling fluid that flows continuously
through the rotary steerable
drilling system 26B. The rotor of the turbine imparts driving rotation to a
drive shaft which is
rotated at a speed that is optimum for turbine operation, though typically
excessive for offsetting
mandrel and bit shaft rotation and having a torque output that is insufficient
for geostationary bit
shaft axis positioning. Thus, a gear train 39, also centrally mounted within
the tool collar 32, has
its input mechanism connected to the turbine driven shaft and has its output
connected to impart
driving rotation to an offsetting mandrel 62. The offsetting mandrel 62, in
the same manner as is
shown in Fig. 14, is provided with a rotary drive head 64 defining an
eccentric positioning
receptacle 66 which receives the upper end 68 of a universally rotatable bit
shaft 70. The bit shaft
70 is mounted within the tool collar 32 by a universal joint 72 in the manner
and for the purpose
described above.
Refernng now to Fig. 16, it should be borne in mind that the scope of the
present
invention is intended to encompass rotary steerable drilling tools having
hydraulically powered
offsetting mandrel rotational control and bit shaft positioning control as
well as turbine/alternator
powered motor control as presented in the embodiments of Figs. 12 and 14. As
shown in Fig. 16,
a turbine 48 is mounted within the tool collar 32 and incorporates a stator 50
and rotor 52, with
the output shaft 54 of the rotor coupled in driving relation with a hydraulic
pump 53. The turbine
48 may be mounted within the tool collar 32 above the electronics and sensor
support section 40
as shown, or below this section. A hydraulic motor 55 is mounted within the
tool collar 32 and is
28
CA 02291600 1999-12-06
operated by pressurized hydraulic fluid from the pump 53 for driving the
offsetting mandrel 62. If
desired, the hydraulic motor SS may incorporate a braking system or have a
braking system in
combination therewith so as to function as a motor and brake in the manner and
for the purpose
described herein. Additionally, the rotary output of the hydraulic motor 55
may be altered by a
gear box 57 so as to provide the desired rotational speed and power for
efficient steering while
drilling.
With reference now to Figs. 17 and 18, the mechanism of the actively
controlled rotary
steerable drilling tool 26 of Fig. 12 is shown in detail and represents the
preferred embodiment of
this invention. Within the lower end of the tubular tool collar 80 there is
defined a bit shaft
support receptacle 82 which is defined by a tubular extension 84 of the tool
collar 80. Within the
receptacle 82 is located a tubular sleeve 86 having a thrust ring 90 which is
spring loaded against
a bit shaft rotation ring 94 and defines a spherical surface segment 92. Bit
shaft rotation ring 94 is
positioned about the bit shaft 96 and defines a corresponding spherical
surface segment 98 that is
in supported engagement with the spherical surface segment 92 of the thrust
ring 90, thus causing
the thrust ring 90 to transfer thrust force from the bit shaft rotation ring
94 to the tubular tool
collar 80 while at the same time allowing the bit shaft to pivot about the
pivot point 99 about
which the spherical surface segment 92 is generated. A segmented retainer 97
is positioned
within a circular retainer groove 101 of the bit shaft 96 and is secured
within the circular retainer
groove 101 by an overlying circular section of the bit shaft rotation ring 94.
A second thrust ring
100 is positioned about the bit shaft 96 and defines a spherical surface
segment 106, in turn
centered about pivot point 99, facing in the same direction as the spherical
surface segment 92 of
the thrust ring 90. The second thrust ring 100 defines a planar thrust
transmitting shoulder surface
102 which is disposed in thrust transmitting engagement with the bit shaft
rotation ring 94 and
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CA 02291600 1999-12-06
with the segmented retainer 97. A second bit shaft rotation ring 104 is
positioned about the bit
shaft 96 and defines a spherical surface segment 107 that is concentric with
the spherical surface
segment 98 and is disposed in thrust force transmitting engagement with the
spherical surface
segment 106 of the thrust ring 100 so as to permit rotation of the bit shaft
96 about the pivot point
S 99 about which both the spherical surface segments 92 and 106 are generated.
The bit shaft
rotation ring 104 is retained in engagement with the thrust ring 100 by means
of a spring that is
positioned by a first ball support ring 108. The thrust rings 90 and 100 can
change location and
diameters with respect to pivot point 99 without departing from the scope of
the present invention.
The chain of thrust rings between the tool collar 80 and the bit shaft 96 is a
preferred
embodiment mechanism which functions to transmit axial forces from the tool
collar 80 to the bit
shaft 96, and to contain bit shaft 96 axially and radially within shaft
support receptacle 82. This
bi-directional force transmission embodiment allows for the bit shaft 96 to
pivot about the pivot
point 99 and permits the axis of the bit shaft to remain geostationary while
rotating in a specified
direction. Alternative methods of transmitting forces include angular contact
radial bearings,
which would also allow for pivoting of the bit shaft about pivot point 99, or
a combination of
tapered thrust rings and angular contact radial bearings which would similarly
allow force
transmission and pivoting.
The first ball support 108 ring defines a circular groove segment surface 110
having a
plurality of pockets in close fitting relation with a plurality of ball
bearings 112 that are received
within spherical bearing grooves 114 in the bit shaft 96. Ball support ring
108 is rotationally
constrained with respect to the tool collar 80 using a plurality of keys or
splines as shown at 211
in Fig. 19. A second circular ball support ring 116 is positioned so that a
circular groove segment
surface 118 thereof defines a plurality of pockets in loose fitting relation
with the ball bearings
CA 02291600 1999-12-06
112 and is also rotationally constrained with respect to the tool collar 80 by
splines 211. The
second ball support ring 116 is in turn supported by a retainer sleeve 120
which is threadedly
secured to the tubular extension 84 of the tool collar 80.
An alternative embodiment for transmitting torque between the collar 182 and
the bit shaft
188 is shown in Fig. 25 where collar 182 transmits torque to the bit shaft 188
through flat or
circular contact surfaces 301 of bit shaft extensions 300. A plurality of bit
shaft extensions 300
can exist, either as integral parts of the bit shaft 188 or as additional
pieces retained in the bit
shaft.
The combination of ball support ring 108, ball bearings 112 and spherical
bearing grooves
114 shown in Figs. 17 and 19 defines a means of transmitting drilling torque
from the tool collar
80 to the bit shaft 96, and in turn to the drill bit. The oversize groove
segment surfaces 110 and
118 in ball support rings 108 and 116 allow for pivoting of the bit shaft 96
about the pivot point
99 while at the same time transmitting drilling torque from the tool collar 80
to the bit shaft 96.
Thus, this embodiment transmits thrust and torque loads between the tool
collar 80 and the
1 S bit shaft 96 while allowing the bit shaft axis to remain geostationary
while being rotated by the
tool collar 80 to achieve drilling in a selected direction.
At its lower end, the tubular tool collar 80 is provided with means for
sealing outside
drilling mud from inside lubricating and protecting oil about the universal
joint. One suitable
means for accomplishing such sealing is a bellows type sealing assembly 126
which creates an
effective barrier to exclude drilling fluid from the universal joint assembly
while accommodating
pivotal movement of the bit shaft 96 relative to the tool collar 80.
Angular positioning of the bit shaft 96 relative to the tubular tool collar 80
is achieved by
an eccentric positioning mechanism shown generally at 128 in Fig. 17. The
offsetting mandrel
31
CA 02291600 1999-12-06
130 is rotatably supported within the tool collar 80 by bearings 142 and is
provided with an
offsetting mechanism to achieve angular offset of the longitudinal axis of the
bit shaft 96 relative
to the longitudinal axis of the tool collar 80. A preferred method for
creating this offset is shown
in Figs. 22A-D, where the offsetting mandrel is attached rotationally to an
outer ring 400 having
an offset internal surface 401, this circular internal surface having a
centerline at an offset and at
an angle to the outside diameter of the inner ring 406 as is more clearly
evident in Fig. 22B. In
Fig. 22A the offsets from the outer and inner rings subtract, which causes the
center of the bit
shaft axis 402 (aligned to internal diameter 407 of the inner ring 406) to be
aligned with the
longitudinal axis of the offsetting mandrel. Consequently, as depicted in
Figs. 22A and 22B, the
center 405 of the inner ring (bit shaft) 406 is coincident with the center 404
of the outer ring
(offsetting mandrel) 404, thereby causing the rotary steerable drilling tool
to drill a straight
wellbore.
If inner ring 406 is rotated 180° relative to the outer ring 400 as
shown in Figs. 22C and
22D, then the resulting geometry of the outer and inner rings 400 and 406 adds
the offsets of the
outer and inner rings, causing the bit shaft axis 402 through point 405 to be
at the maximum offset
403 with respect to the outer ring 400, thus locating the bit shaft at its
maximum angle with
respect to the drill collar to drill in a desired direction. To achieve a
lesser angle of the bit shaft
with respect to the tool collar than occurs with the ring setting of Figs. 22C
and 22D, the bit shaft
positioning rings can have any relative rotational positioning between the
ring positions of Fig.
22A and 22B and the ring positions of Figs. 22C and 22D to thus drill a bore
having a lesser
degree of curvature being determined by the relative positions of the rings
400 and 406. Thus, the
angled relation of the longitudinal axis of the bit shaft with respect to the
longitudinal axis of the
drill collar is variable between 0° and a predetermined maximum angle
depending upon the
32
CA 02291600 1999-12-06
relative positions of the bit shaft positioning rings. These rings can be
rotated with respect to each
other by various mechanical or electrical means, including but not limited to
a geared motor.
It should also be borne in mind that one of the rings of the offsetting
mechanism can be
defined by the eccentric receptacle 134 of the concentric drive element 132 at
the lower end of the
offsetting mandrel 130 as shown in Fig. 17. As the eccentric receptacle 134 of
the offsetting
mandrel 130 is rotated by the concentric drive element 132 the eccentric
receptacle 134 subjects
the upper end of the bit shaft 96 to lateral positioning with respect to the
axis of rotation of the
offsetting mandrel 130 as determined by the relative positions of the rings
400 and 406 of Figs.
22A-22D, thus causing the bit shaft 96 to be rotated about its universal
support so that its
longitudinal axis 133 becomes positioned in angular relation with the axis of
rotation 135 of the
tubular tool collar 80 as shown in Fig. 17. Since the offsetting mandrel drive
motor, whether
electric; hydraulic or a drive turbine, counter-rotates the tubular drive
shaft and the concentric
. drive element of the offsetting mandrel 130 at the same rotational frequency
as that of the tubular
tool collar 80, the concentric drive element 132 maintains the longitudinal
axis 133 of the bit shaft
96 at a geostationary angle with respect to the axis of rotation of the
tubular tool collar 80. Since
the tool collar 80 is in direct rotational driving relation with the bit shaft
96, rotation of the tool
collar 80 by the drill string or by a mud motor connected to the drill string,
causes the bit shaft 96
to rotate the drill bit supported thereby at the angle of inclination and
azimuth that is established
by such orientation of the bit shaft. This causes the drill bit to drill a
curved borehole that is
permitted to continue its curvature until such time as a desired borehole
inclination has been
established. The drilling tool is then controlled by signals from the surface
or by feedback signals
from its various on-board control systems such that its steering control
mechanism is neutralized
and the resulting borehole being drilled will continue straight along the
selected angle of
33
CA 02291600 1999-12-06
inclination and azimuth that has been established by the curved borehole. The
"ring within a ring"
bit shaft adjustment feature facilitates bit shaft angulation adjustment as
drilling operations are in
progress, without necessitating cessation of drilling or withdrawal of the
drilling equipment from
the wellbore.
S To accommodate pivoting excursion of the bit shaft 96 without interfering
with fluid flow
through the flow passage 148 of the bit shaft, the offsetting mandrel 130 is
provided with an offset
flow passage section 150 which directs flowing drilling fluid from the flow
passage 152 of the
tubular drive shaft and permits unrestricted flow of drilling fluid through
the offsetting mandrel
130 even when the bit shaft 96 has been positioned thereby for its maximum
angle with respect to
the tool collar 80. A tubular pressure compensator 154 is positioned about the
offsetting mandrel
130 as shown in Fig. 18 and separates an oil chamber 158 from an annular
chamber 159 and is
intended to contain a protective oil medium within the oil chamber 158. The
pressure
compensator 154 is connected and sealed to the lower end 164 of a tubular
electronics carrier 166
which is also shown in the cross-sectional illustration of Fig. 20. The
tubular electronics carrier
166 defines a weighted section 168 extending circumferentially in the range of
about 90 degrees
as shown in Fig. 20 and providing for retention of various system control
components such as a
magnetometer, a gyroscopic device, an accelerometer, a resistivity sensor
arrangement and the
like. Additionally, the weighted section 168 provides counterbalancing forces
during shaft
rotation to offset the lateral loads of rotary bit shaft actuation and thus
minimize vibration of the
rotary steerable drilling tool during its operation. A partial circumferential
space 170 is defined
internally of the tool collar 80 and externally of the tubular electronics
carrier 166 and provides
for location of the system electronics 172 of the rotary steerable drilling
tool. The system
electronics 172 and the various system control components are counter-rotated
by the drive motor
34
CA 02291600 1999-12-06
at the same rotational speed as that of the tool collar 80 so that the
electronics and system control
components are essentially geostationary during drilling operations.
Referring now to Fig. 21, an alterative embodiment of the present invention
having a
splined universal joint is shown generally at 180, having a tool collar 182
that is adapted for
S connection to a drill string for rotation in the manner described above. The
tool collar 182 defines
an elongate tubular extension 184 which defines an internal receptacle 186
having an
omnidirectional drive connection or universal joint located therein for
permitting angulation of the
bit shaft 188 with respect to the tool collar 182 for geostationary
positioning of the bit shaft and
drill bit for drilling a curved wellbore. A shoulder within the internal
receptacle 186 provides
support for a thrust ring 190 having a spherical surface segment 192. A bit
shaft rotation ring 194
is located about the bit shaft 188 and defines a spherical surface segment 196
that is disposed in
force transmitting and pivotally movable relation with the thrust ring 190.
The bit shaft rotation
ring 194 defines a circular recess within which is positioned a circular
thrust flange 200. A
second thrust ring 204, also encompassing the bit shaft 188, is positioned
with one axial end
1 S thereof disposed in abutment with the circular thrust flange 200 and the
bit shaft rotation ring
194. The lower circular face of the second thrust ring 204 is defined by a
circular spherical
surface segment 206, being a segment of a sphere that is concentric with the
spherical surface
segment 192. The circular spherical surface segment 206 is engaged by an
external upwardly
facing spherical surface segment 207 of a lower thrust ring 208 so that
positioning of the
longitudinal axis of the bit shaft 188 relative to the longitudinal axis of
the tool collar 182 occurs
about pivot point 209.
Control Architecture
Refernng now to Fig. 23, the system control architecture of the rotary
steerable drilling
CA 02291600 1999-12-06
system of the present invention is shown by way of block diagram illustration.
The system
electronics 240 incorporate a programmable electronic memory and processor 242
which is
programmed with appropriate algorithms for desired toolface calculation,
establishing the
borehole curvature that is desired to steer the borehole being drilled to a
subsurface zone of
interest. The system electronics is programmable downhole and programmable
during drilling to
enable drilling personnel to selectively steer the drill bit as drilling is in
progress.
As steerable well drilling is in progress various data is acquired and input
to the system
electronics for utilization in toolface calculation. Data from magnetometers
244 provides the
system electronics with the position of the tool collar with respect to the
earth's magnetic field.
Data from one or more gyroscopic sensors 246 provides the system electronics
with the angular
velocity of the output shaft, i.e., the bit shaft of the rotary steerable
drilling system. For purposes
of control, the data from the magnetometers and gyroscopic sensors is
available to the system
electronics by selection of an OR gate circuit 248 which is capable of
automatic actuation by the
system electronics and selective actuation by control signals from the
surface. At least one and
preferably a plurality of accelerometers 250 are provided within the rotary
steerable drilling
system and provide data input to the system electronics that identifies the
position of the tool
collar in real time with respect to gravity.
Utilizing the various data input from the magnetometers, gyroscopic sensors
and
accelerometers, the system electronics 240 calculates the instantaneous
desired angle between the
scribe line of the tool collar and the scribe line of the offsetting mandrel
and transmits signals to a
motor controller 252 representing the desired angle.
An angular position sensor 260, a resolver for example, is located within the
tubular tool
collar and is positioned in non-rotatable relation about a portion of the
drive shaft of the brushless
36
CA 02291600 2004-09-15
50952-14
direct current motor/brake 256 which is capable of
rotationally driving the offsetting mandrel or rotationally
braking the offsetting mandrel as controlled by the system
electronics 240 responsive to various signal input. The
purpose of the angular position sensor or resolver 260 is to
identify the real time position of the motor/brake shaft at
any given point in time relative to the tool collar and to
communicate motor/brake position signals to the motor
controller 252 via signal conductor 257. It should be borne
in mind that the motor shaft is driven in a rotary direction
that is counter to the rotation of the tubular tool collar
by the drill string to which the tubular tool collar is
connected and at the same frequency as the rotational
frequency of the tool collar. The angular position sensor
or resolver may take the form that is shown and described in
U.S. Patent 5,375,098. The output shaft of the
motor/brake 256 drives a gear box 262 to thus permit the
motor to operate at its optimum rotational speed for desired
torque and to permit the output shaft 258 to be rotated in
synchronous relation with the speed of tool collar rotation.
A switch/trigger 264, such as a Hall effect sensor or other
trigger circuit, is provided which, when triggered, provides
the actual position of the offsetting mandrel with respect
to the tool collar. The signals of the switch/trigger are
input to the motor controller 252 via signal conductor 265
to identify the bit shaft position change, if any, that is
necessary for the drill bit to follow a programmed curved
track during steerable drilling operations. Alternatively,
the angular position sensor 260 may be mounted on the output
shaft of the gear box 262.
With reference now to Fig. 24, the system control
architecture for the alternative embodiment of Fig. 14 is
shown wherein the motive force for counter-rotational
37
CA 02291600 2004-09-15
50952-14
control of the offsetting mandrel and thus geostationary
positioning of the axis of rotation of the bit shaft is
achieved by a drilling fluid powered turbine and brake and
is controlled in part by controlling the
37a
CA 02291600 1999-12-06
efficiency of the turbine. That portion of the system control architecture,
for establishing a
control signal representing the desired angle between the scribe line of the
tool collar and the
scribe or reference line of the offsetting mandrel is substantially of the
form that is described
above in 'connection with Fig. 23. This angle control signal is supplied to a
brake controller 266
which also receives position signal input via trigger signal conductor 268
from a trigger circuit
270 and via a resolver signal conductor 272 from a resolver 274. The control
signal output of the
brake controller 266 is supplied to an efficiency control circuit 276 for
controlling the efficiency
of the turbine 278 and is supplied to a brake 280 for controllably braking the
output shaft of the
turbine 278 and thus for controlling rotation of the shaft that is sensed by
the resolver. To ensure
that the turbine rotated and brake controlled shaft, typically the offsetting
mandrel, is rotated at
the proper speed for efficient positioning control of the bit shaft, a gear
box 280 may have its
input connected with the turbine driven and braked shaft and may be
appropriately geared to drive
its output shaft 282 within the desired speed range for efficient bit shaft
positioning and efficient
curved borehole drilling.
An alternative option is to include within the system a turbine control
mechanism capable
of modifying the power produced by the turbine by changing its efficiency. As
shown at 276 and
278 in the block diagram system control architecture of Fig. 24 and
schematically in Fig. 13, this
feature can be achieved by housing the rotor 52 of the turbine 48 in a stator
50 defining a conical
surface 53, and by moving the stator 50 linearly with respect to the rotor 52,
thus defining a
selectively variable turbine. The mounting system for the turbine 48 within
the rotary steerable
drilling tool will cause the stator 50 to be mounted within the tool collar
for controlled linear
movement responsive to the system electronics and brake controller. The
mounting system for
the stator is actuated by the control electronics of the drilling tool, i.e.,
position signal responsive
38
CA 02291600 1999-12-06
brake controller 266 and efficiency control 276 as shown in Fig. 24, so that
its adjustable
positioning can be achieved with the drilling tool located downhole and can be
achieved while the
drilling tool is in operation to effectively maintain rotational speed and
torque of the turbine
within desired limits for effective operation.
Such a turbine control mechanism would be used to reduce the power output of
the turbine
at higher flow rates. At lower flow rates the turbine would work at its
maximum efficiency to
insure that the turbine power is always larger than the resistive power. Since
the turbine control
mechanism would mainly respond to flow rate variations its response bandwidth
need not be very
high.
In view of the foregoing it is evident that the present invention is one well
adapted to
attain all of the objects and features herein set forth, together with other
objects and features
which are inherent in the apparatus disclosed herein.
As will be readily apparent to those skilled in the art, the present invention
may easily be
produced in other specific forms without departing from its spirit or
essential characteristics. The
present embodiments are, therefore, to be considered as merely illustrative
and not restrictive, the
scope of the invention being indicated by the claims rather than the foregoing
description, and all
changes which come within the meaning and range of equivalence of the claims
are therefore
intended to be embraced therein.
39
